Today, as a wireless system technique for high-speed transmission using a millimeter waveband, the WirelessHD standard has been established, and such a wireless system technique is being standardized for existing wireless local area networks (in particular, the 802.11a/b/g networks).
It is problem for a wireless system using a millimeter waveband to coexist with other wireless systems on the same frequency band.
In order for different wireless systems to coexist on the same frequency band, a given wireless system needs to recognize interference (to be referred to as “giving interference” hereinafter) which is given by the system to another wireless system (for example, a system conforming to the wirelessHD standard, a wireless LAN system being standardized, or the like) and/or interference (to be referred to as “receiving interference” hereinafter) which is received at the system from the other wireless system, and to perform processing (for example, processing of switching a frequency channel) for coexisting with the other wireless system on the same frequency band based on the recognized giving interference situation and/or receiving interference situation.
Conventionally, processing of recognizing an giving interference situation and/or receiving interference situation with the other wireless system and processing for coexisting with the other wireless system are under consideration in cognitive communication. For example, a method of estimating an giving interference situation, a method of determining a channel to be used, and the like are considered. In this case, each wireless communication apparatus in a given wireless system receives a signal transmitted/received by another wireless system coexisting on the same frequency band, and uses control information contained in the received signal to determine whether to change a frequency channel to be used. For example, each wireless communication apparatus estimates, based on a received power, an antenna gain, amplifier gain information, and the like, whether transmission by itself has an influence on a wireless communication apparatus in another wireless system. If the apparatus estimates that transmission has an influence, it determines to change a frequency channel; otherwise, it determines not to change a frequency channel. Alternatively, for example, each wireless communication apparatus estimates, based on scheduling information of another wireless system, whether there is a time during which the apparatus itself can transmit/receive a signal without influencing any wireless communication apparatus in the other wireless system. If the apparatus estimates that there is no such time, it determines to change a frequency channel; otherwise, it determines not to change a frequency channel.
This technique, however, has a disadvantage that it is necessary to recognize contents of control information by receiving a signal transmitted/received in another wireless system, and decoding the received signal.
In contrast, in a conventional wireless LAN, access control is performed in CSMA/CA scheme. According to the access control, each wireless communication apparatus measures and detects the occupancy status of a wireless channel before using it, and sets random backoff before transmission, thereby enabling a plurality of wireless communication apparatuses to fairly use a band.
On the other hand, as a method which emphasizes facilitation of connection and an improvement in efficiency, there is considered a technique of performing, by assuming a one-to-one connection, random backoff in transmitting a control signal until a connection is established, and transmitting/receiving a signal at a regular interval (for example, an SIFS, a DIFS, or the like in an IEEE 802.11 wireless LAN) without backoff after the connection is established.
If, for example, to increase the speed of transmission/reception, frames are transmitted using a short interframe space as compared with other interframe spaces for a given period after a connection is established, a wireless communication apparatus in another wireless system cannot transmit/receive a signal depending on the giving interference/receiving interference relationship with the other wireless system. That is, assume that the other wireless system is a wireless LAN system which detects the occupancy status of a wireless channel before using it. In this case, if frames having short interframe spaces are successively transmitted, the wireless communication apparatus in the other wireless system detects a busy state, thereby disabling to transmit/receive a signal while the frames are successively transmitted. This causes a problem that fairness is not ensured.
Conventionally, there is unknown a technique which enables a given wireless system to estimate an giving interference situation and receiving interference situation without receiving and decoding a signal transmitted/received in another wireless system on the same frequency band, and to select, based on the estimation result, processing necessary for coexisting with the other wireless system while ensuring fairness for the other wireless system.